The applicants have observed an increased rate of apoptosis of both microvascular pericytes and endothelial cells in the retinas of diabetic individuals as an antecedent to the formation of acellular nonperfused capillaries, which coincides with decreased synthesis of IGF-I. They hypothesize that IGF- I may act as a survival factor for retinal vascular cells. To investigate the role of apoptosis in diabetic retinopathy, endogenous regulators such as Bcl-2, Bcl-x, and Bax will be examined in human diabetic and nondiabetic retinal microvessels and in galactosemic rats. Cell proliferation markers, such as proliferating cell nuclear antigen (PCNA), Ki-67 (which is absent in resting cells and during DNA repair) and the length of telomeric DNA, will be compared in diabetic and nondiabetic retinal microvessels as indicators of the ratio of decreased replicative capability to accelerated turnover. They hope to ascertain a role for IGF-I deficiency by characterizing its signalling system in human diabetic microvessels and in those of galactosemic rats and through IGF-I deprivation by the use of transgenic IGF-I knockout mice or by interference with IGF-I signal transduction. VEGF and transforming growth factor- beta (TGF-beta) will also be examined in these tissues to determine if their expression is modified in diabetes. Lastly, cell cultures of retinal microvascular pericytes and endothelial cells will be used to determine whether elevated hexose can initiate apoptosis (and if so, by what mechanism) and/or have an effect on the expression of IGF-I.